How big is the universe?
No one knows the full size of the universe, and it may be infinite. The observable universe, the part we can see, is about 93 billion light-years across.
Light travels at a fixed speed, and the universe is about 13.8 billion years old, so we can only see objects whose light has had time to reach us. Because space has been expanding the whole time, the most distant regions we can see are now about 46 billion light-years away in every direction, giving a diameter of about 93 billion light-years.
Beyond that boundary, the universe almost certainly continues, but its light has not reached us yet. Measurements of the cosmic microwave background suggest that space is very close to flat on large scales, which is consistent with a universe that is either infinite or far larger than the part we can observe.
Still growing
The universe is not only big but also expanding, and the expansion is speeding up. Astronomers think a mysterious force called dark energy is behind this acceleration. As a result, the most distant galaxies are moving away from us so fast that their future light may never reach Earth.
Did You Know?
The observable universe contains an estimated hundreds of billions to two trillion galaxies, each with millions to trillions of stars.